Most physiological relevant targets for CaM are proteins, but CaM also binds to a number of peptide hormones, toxins, and peptides, which represent CaM binding domains, as well as small drug-like molecules [55-57]. Melittin, a small hydro-phobic peptide from bee venom consisting of 26 amino acid residues, is known to bind Ca2+-saturated CaM (holo-CaM) in a 1:1 ratio with a range of Kd values between 3 nM  and 110 nM . The low molecular weight of melittin (MW 2845), its a-helical structure , and its high affinity for CaM make it a good candidate for detailed structural studies of CaM-target recognition. Although the me-littin model has some drawbacks, there is phenomenological evidence [61, 62] that the binding of melittin to CaM resembles that of myosin light-chain kinase protein (MLCK)  and troponin I . Binding the third and fourth Ca2+ becomes more endothermic, but the free energy coupling in the CaM-Ca2+-melittin system is entropically driven by hydrophobic interactions (i.e. by significant dehydration of nonpolar groups in the Ca2+ -binding sites and in the two surface-
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